Today, my blood sugar was a little high when I woke up. Normally I would simply take more insulin to bring it down. But I knew I wanted to go for a run soon. Working off my past experiences, I thought about how to strike the right balance of insulin, food and exercise in relation to my blood sugar. It would be great to have a system for managing this situation that removes the guesswork for patients.
The challenge of keeping my blood sugar under control during exercise.
Exercise and insulin both lower blood sugar. So I need to adjust these variables and/or my food to keep my blood sugar in range.
Lately my normal exercise is a 5 miles run lasting about 40 minutes.
I use Humalog rapid-acting insulin. According to the manufacturer Eli Lilly, “In healthy volunteers given subcutaneous doses of HUMALOG ranging from 0.1 to 0.4 unit/kg, peak serum levels were seen 30 to 90 minutes after dosing.” (emphasis mine) Attached are two charts, also provided by Eli Lilly, comparing Humalog and Regular insulin.
I use a MiniMed 522 insulin pump. There are two main ways that the pump delivers insulin:
- basal rates
- bolus dosages
I have variable basal rates throughout the day. During my waking hours, the rate stays the same. Right now, I am set to .55 u/hour from 6:30am to midnight. Once you program your pump, it automatically injects this insulin throughout the day.
Bolus dosages are taken to cover meals or to lower blood sugar when it is too high. They are programmed manually by the patient. When trying to decide how much insulin to take with a meal, it is helpful to determine the carb total for the food. Most of the insulin is needed to cover this. Many patients figure out their insulin-to-carb ratio, then can determine the appropriate bolus dosage.
I could eat different amounts or types of food in preparation for exercise.
I have three main ways of dealing with my blood sugar for a run of this type.
- Dial down my basal rate (1 hour before I head out)
- Take a smaller bolus dose (for a meal I eat before running)
- Do nothing (when my blood sugar is high before the run)
Each course of actions have some variables to determine.
For Option 1, I choose to dial down my basal rate for an hour mostly because this has worked in the past (trial-and-error). It also takes into consideration the Humalog information I presented above. If the insulin takes about an hour to kick in but has been reduced an hour before exercise, it is not pushing blood sugars down at a time when the exercise is.
Lately, I have been dialing down from .55 u/hour to .05 u/hour for an hour immediately before I head out. But the variables/unkowns are:
- Best length of time for the temporary basal rate
- The appropriate temporary basal rate compared to the normal basal rate (reduce by what percentage?)
- The timing of the start and end of the temporary basal rate (in relation to the time, length and intensity of the exercise)
- How these variables change with changes in exercise type/duration/intensity
With a run of this length, this approach seems fine. But it tends to get more complicated when the runs get longer. I use this method mainly when I am running at night or during the day.
I use Option 2 mostly when I run in the morning. I don’t want to deal with getting a temporary basal rate going while I am sleeping, which seems complicated. My standard breakfast these days is an English muffin, for which I normally take 3.0 – 3.5 u. But when I am about to do this type of run, I take about 1 unit less and start my run about 45 minutes after eating. Things get more complicated if I do a longer run however. Unknowns are:
- Amount to reduce bolus dosage
- Timing for dosage, eating and the start of the run
- Time range that this method is effective.
Option 3, which I just used today, is less common. Normally I normally try to get my blood sugar level down right away when I see it is high. But I knew I wanted to take a run, so I dealt with it that way. Unknowns include:
- Amount that blood sugar will drop in relation to the specifics of the exercise
- Drop in blood sugar for runs longer than an hour (since basal rates are still kicking in during the exercise)
In the near future, I will present to you more of the specifics on my blood sugar levels before, during and after runs this year using these three methods.